Under the March 2016 deal between the EU and Turkey, Ankara pledged to take back any illegal migrants who arrived in the Union after departing its territory and instead send legal Syrian refugees to the bloc.

A new BBC2 documentary has revealed that German Chancellor Angela Merkel's private talks with Turkish officials in 2016 to discuss the flow of migrants into the EU infuriated European Council President Donald Tusk, who warned that the Ankara-Brussels migration deal "would be a catastrophe".